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July 21, 2011 -- There is an ongoing "explosion" of deadly hepatitis C among men who have sex with men.

It's spread mainly by anal sex, often enhanced by methamphetamine, according to a report in the July 21 issue of the CDC's Morbidity and Mortality Weekly Report.

"We are having an explosion of sexually transmitted hepatitis C," study researcher Daniel S. Fierer, MD, of New York's Mount Sinai School of Medicine, tells WebMD. "We have uncovered an emerging epidemic of sexual transmission of hepatitis C. And the main reason is men having anal sex without a condom."

It's no surprise to experts who treat hepatitis C. Liver cancer and cirrhosis caused by hepatitis C virus (HCV) already is the leading cause of death among people with HIV infection who have access to HIV drugs. Some 30% of Americans with HIV are co-infected with HCV.

Sexual transmission of HCV among people without HIV is rare, notes Eugene R. Schiff, MD, director of the Center for Liver Diseases at the University of Miami, who was not involved in the Fierer/CDC study. Among heterosexual couples, he says, only 2% of those with HCV infect their partners after 20 years of monogamous marriage.

The same may be true for men who have sex with men -- if they practice safe sex.

"Our data do not support sexual HCV transmission between HIV-negative men," Fierer says. "There is reasonable data that HIV-negative men are not part of this epidemic."

But that's not the case for HIV-positive men, notes Lynn E. Taylor, MD, of Brown University. Taylor was not involved in the Fierer study. In a study published last March, Taylor and her colleagues showed that new HCV infections are relatively common among HIV-positive men who do not use intravenous drugs -- a phenomenon previously reported in Europe and Australia.

"We have robust evidence of increasing HCV incidence among men who have sex with men who do not inject drugs but do engage in high-risk sexual behaviors," Taylor, who was not involved in the Fierer study, tells WebMD. "It is the new sexually transmitted infection in this population. I am very concerned."

Schiff notes that when HIV-positive men get HCV, they have much higher levels of the hepatitis C virus in their blood. Taylor and Schiff warn that hepatitis C infection progresses quickly in people with HIV infection.

"These men are sitting ducks for liver cancer," Taylor says. "If they don't get treated and get HCV eradication, they are at risk of cirrhosis or liver cancer. ... We are seeing tons of gay men newly diagnosed with HIV, and then with HCV. I could go to a funeral of an HCV patient every week."

Anal Sex, Methamphetamine Linked to HCV

Fierer and colleagues gave detailed questionnaires to 34 HIV-positive men with new hepatitis C infections, as well as to 67 closely matched HIV-positive men who tested negative for HCV. In detailed questioning and interviews, the men denied any form of intravenous drug use -- even the use of prescription testosterone.

There was "quite a laundry list" of behaviors linked to new HCV infections. But careful statistical analysis revealed two factors that independently raised an HIV-positive man's risk of HCV infection:

Having sex while high on methamphetamine increased HCV risk 28.5-fold.

"This is a smoking gun for classic sexual transmission with semen," Fierer says.

Fierer warns that while the study implicates semen, it does not suggest that anal sex without ejaculation is safe. It isn't. And a troubling study of outbreaks of HCV among HIV-positive German men suggested last March that prolonged or traumatic anal intercourse often exposes both partners to infected blood.

As for methamphetamine, Fierer says the problem is that it removes sexual inhibitions while prolonging the sex act.

"Crystal meth is an incredibly disinhibiting drug. This is very much used for sex, and judgment and all kinds of other things go out the window," he says. "Patients tell me, 'Well, now it seems like a very bad idea to take meth and have unprotected sex with a partner who ejaculates in you. But at the time it seemed like a great idea."

Taylor warns that using erectile dysfunction drugs to prolong sex also appears to be a risk factor for HCV transmission among HIV-positive men.

Sex-Spread HCV Threatens New HCV Treatments

New HCV treatments make it much more likely that a person can be cured of hepatitis C. But there's a catch.

Schiff notes that a person can be infected with hepatitis C over and over again. He's already seen patients who seem to be getting better with treatment, and then suddenly are reinfected.

That's going to be a problem, he says, because powerful new hepatitis C drugs have an Achilles heel -- the virus quickly becomes resistant. If a person is reinfected with HCV during treatment with one of the new drugs, there's a good chance the virus will acquire resistance to all similar drugs.

"If people are re-exposed to HCV after treatment with new antivirals, there will be resistant virus," he predicts.

Taylor predicts the same thing.

"The rates of HCV reinfection in HIV-positive men appear to be much higher than in other groups," she says. "So just like syphilis, they come in with hepatitis C again and again. ... [It is] a definite reality we are going to be dealing with drug-resistant hepatitis C by the end of this year."